AU2005297158A1 - Screw and fastening system for profiled sheeting - Google Patents

Description

WO 2006/043169 PCT/IB2005/003163 SCREW AND FASTENING SYSTEM FOR PROFILED SHEETING 5 Field of the Invention This invention concerns the use of self-drilling threaded screw fasteners and has particular relevance to screws for affixing sheet metal roofing and cladding to thin metal battens in an underlying structure. It is especially useful with the newer 10 generation of battens which are made from thin gauge high strength steels. The invention also concerns the manufacture of a novel type of threaded fastener for use in the above-described situations. Preferred embodiments of the fastener are also adapted for self-drilling and fastening into timber components. 15 Background to the Invention It is well known to fasten profiled architectural sheet steel roofing and cladding sheets to underlying roll-formed steel battens by use of self-drilling threaded fasteners. The 20 fasteners are typically fastened through a rib on the sheet and have a rubber seal fitted for weatherproofing. Examples of such profile sheets are conventional corrugated steel sheet and proprietary profiles sold in Australia under the trade marks CustomOrb, Trimdek and Spandek. 25 However the recent introduction of battens made from thinner gauge higher strength steels than used previously has made it more difficult for existing screws to function reliably. The steels used in those new type of battens have nominal strengths of 450 MPa and higher. Sometimes manufacturing variability means strengths as high as 700 MPa are seen in samples of steel sold as having much lower strength. 30 Problems have been encountered when using self-drilling fasteners having conventional tips to drill through sheets of such high strength steels. Conventional WO 2006/043169 PCT/IB2005/003163 2 steel drilling tips do not easily start drilling into the metal. A Type 17 tip, which has a hardened sharp point can drill through earlier generations of battens but, when used against a high strength steel, often becomes blunt and thus ineffective within the first 3 or 4 rotations of the fastener, so the tip does not even commence penetrating into 5 the harder sheet steels. In addition the increasingly thinner gauges of steel used for the battens also causes an increased tendency for conventional screws to pull out because an insufficient bearing area of fastener thread is engaged with the thickness of the batten. 10 Furthermore, some conventionally used self-drilling screws create a burr around the hole in the sheet metal. This burr has three major disadvantages: - it can damage the rubber seal, so leading to leakage, - it can lay across the seal, so providing a path for water to bypass the seal, and 15 - it is prone to corrosion, so leading to discolouration of the sheet's surface and premature corrosion of the parent metal around the hole. An aim of one aspect of the present invention is to provide a screw fastener which overcomes the above-described difficulties relating to ability to penetrate the higher 20 strength battens, pullout strength and burning of the sheet metal. The invention is particularly useful for attaching components to a batten or other support which has a metal thickness in the range 0.35mm to 1.2mm, and particularly 0.45mm to 1.0mm, and a strength higher than 300 MPa. 25 A further aim is to provide such a screw fastener which, while particularly adapted for fastening to thin metal battens, is also suitable for fastening into hardwood and softwood supports as well as into other metal structures. In this way a single screw type can have wide applicability. 30 An aim of another aspect of the invention is to provide a method for manufacturing such screws.

WO 2006/043169 PCT/IB2005/003163 3 Summary of the Invention Accordingly, in one aspect the invention provides a screw fastener for attaching a 5 profiled sheeting panel to a support, said fastener having: (i) an elongate shank; (ii) an enlarged head at one end of the shank adapted for engagement with a driving tool; (iii) a drilling tip on the other end of the shank adapted to drill a hole of a first 10 diameter; (iv) on the shank a first threaded portion adapted to screw into said support, said first threaded portion having a first thread, the crest of said first thread defining a major diameter of the first thread, and the root of said first thread defining a minor diameter of the first thread; 15 (v) said drilling tip sized such that said first diameter is in the range of 60% to 85% of the minor diameter; (vi) a tapered portion joining the drilling tip to the first threaded portion said tapered portion having a tapered thread thereon, said tapered thread having a thread height which increases from the drilling tip to said first threaded 20 portion; (vii) on the shank a second threaded portion adapted to engage a crest of said panel; and (viii) a reaming portion located between the first threaded portion and the second threaded portion, said reaming portion having an outside diameter less than 25 said major diameter of the first thread. The drilling tip preferably has a generally cylindrical cross section and two diametrically opposed flutes which extend in the axial direction of the fastener. The flutes preferably intersect thread formed on the drilling tip. 30 Each flute may terminate at a cutting edge, said cutting edges subtending therebetween an angle in the range 1300 to 150*.

WO 2006/043169 PCT/IB2005/003163 4 In another aspect the invention provides a method of fixing a profiled architectural sheet to a support member whereby a threaded fastener passes through said sheet and into the support member, said fastener comprising: 5 - an elongate shank having an enlarged head at one end and a drilling tip on its other end; - a first threaded portion positioned towards said other end, the thread of said first threaded portion having a major diameter and a minor diameter; - a second threaded portion separated from said first threaded portion and 10 located between said head and said first threaded portion; - a tapered threaded portion adjacent and between the drilling tip and the first threaded portion; and - a reaming portion located between said first threaded portion and said second threaded portion; 15 said method comprising: (i) rotating the fastener with said drilling tip pressed into contact with a rib on said sheet; (ii) causing the drilling tip to cut a first hole of a first diameter by removing metal from said sheet; 20 (iii) rotating the fastener into the first hole to engage said tapered threaded portion with said sheet; (iv) rotating the fastener further into the first hole to expand said first hole by plastic deformation of the metal immediately surrounding the hole, thereby increasing the thickness of the metal immediately surrounding the hole and 25 increasing the diameter of the hole; (v) continuing to rotate the fastener into the first hole, thereby: - skimming the reaming portion through said first hole to increase the diameter of the hole to less than said major diameter, and - causing the drilling tip to cut a second hole of said first diameter in 30 the supporting member; (vi) continuing to rotate the fastener further into said second hole to engage said tapered threaded portion with the support member; WO 2006/043169 PCT/IB2005/003163 5 (vii) continuing to rotate the fastener further into the second hole to expand the second hole by plastic deformation of the metal immediately surrounding the second hole, thereby increasing the thickness of the metal immediately surrounding the second hole and increasing the diameter of the second hole; 5 and (viii) continuing to rotate the fastener into the first and second holes to thereby engage said first threaded portion with said supporting member and engage said second threaded portion with said sheet. 10 The cutting of said second hole by the drilling tip may commence before or after the reaming portion commences the skimming through said first hole. Each flute may terminate at a cutting edge, said. cutting edges subtending therebetween an angle in the range 1300 to 150". The angle is preferably in the range 15 1300 to 1450 and more preferably in the range 1300 to 1400. In a further aspect the invention provides a method of manufacturing a self drilling threaded fastener including: - forming a tipped blank having an unthreaded shank, an enlarged head at 20 one end and a drilling tip at the other end, said drilling tip having a generally cylindrical cross section of diameter smaller than the diameter of said unthreaded shank, said drilling tip having two diametrically opposed flutes which extend in the axial direction of the fastener, and said drilling tip being joined to said unthreaded shank by a tapered portion; and 25 - roll forming onto said tipped blank: - a first threaded portion toward the tip end of said tipped blank, - a second threaded portion toward the head end of said tipped blank, and - a knurled portion located between the first and second threaded 30 portions and having the size of its outside diameter between the minor diameter of the first threaded portion and the major diameter of the second threaded portion; WO 2006/043169 PCT/IB2005/003163 6 wherein said first threaded portion includes: - a third threaded portion having a parallel thread formed onto said shank, - a fourth threaded portion formed onto said drilling tip and intersected by said flutes, and 5 - a tapered threaded portion joining said third and fourth threaded portions. In a further aspect the invention provides a self-drilling threaded fastener adapted for fastening a high strength sheet steel architectural panel to a support, and having a drilling tip wherein the drilling tip comprises a portion having two diametrically 10 opposed flutes which extend generally in the axial direction of the screw, each said flute terminating at a cutting edge said cutting edges subtending therebetween an angle in the range 130* to 1500. The angle is preferably in the range 1300 to 145" and more preferably in the range 1300 to 140*. 15 In a further aspect the invention provides a screw threaded fastener including an elongate shank having a longitudinal axis, an enlarged head at one end of the shank, a leading tip at the opposite end of the shank, and a screw thread extending over at least a part of the length of the shank, wherein the screw thread includes: - a root and a crest; 20 - a leading flank rising from the root and directed away from the leading tip and sloping outwardly relative to the longitudinal axis at a varying angular disposition relative to the longitudinal axis; - a trailing flank rising from the root and directed away from the head and sloping outwardly relative to the longitudinal axis at a varying angular 25 disposition relative to the longitudinal axis, - said leading flank and trailing flank joining at said crest of the screw thread; wherein: - the angular disposition of the leading flank relative to the longitudinal axis 30 changes between the root and the crest from greater than 450 nearer the root to less than 450 nearer the crest; and WO 2006/043169 PCT/IB2005/003163 7 - the angular disposition of the trailing flank relative to the longitudinal axis changes between the root and the crest from less than 450 nearer the root to greater than 450 nearer the crest. 5 The angular disposition of one or both flanks relative to the longitudinal axis may change gradually whereby that flank would have a gradually curved form when viewed in cross section longitudinal to said axis. Alternatively the angular disposition of one or both flanks relative to the longitudinal axis may change abruptly at one or more points. 10 The rate of change of the angular disposition of a flank relative to the longitudinal axis may be substantially constant. A flank may appear to be uniformly curved from root to crest. Alternatively a flank may appear to be curved non- uniformly from root to crest. 15 Alternatively a flank may be faceted with a facet edge extending along the thread in a helical direction coaxial with said longitudinal axis. The trailing flank may therefore appear dished. The trailing flank may be concave 20 from said root of the thread to the crest of the thread. It may have a gently curved concave form or may comprise a plurality of generally flat segments when viewed in cross section. The leading flank may appear vaulted. It may have a domed or gently convex form or 25 may comprise a plurality of generally flat segments when viewed in cross section. Brief Description of the Drawings Examples of the invention will now be described with reference to the attached 30 drawings where: Figure 1 is a side elevation view of a screw which is a threaded fastener according to one embodiment of the present invention; WO 2006/043169 PCT/IB2005/003163 8 Figure 2 is a cross section of the head portion of the screw shown in Figure 1; Figure 3 is an end view of the head of the screw shown in Figure 1; Figure 4 is an enlarged view of the tip of the screw in Figure 1 when viewed from the direction opposite to that of Figure 1; 5 Figure 5 is a cross-section view through plane A-A as indicated in Figure 1; Figure 6 is a cross-section of portion of the screw thread form in the region marked "B" in Figure 1; Figure 7 is a diagrammatic view of a screw according to the invention part-way through the process of its manufacture; 10 Figure 8 is a view of the screw in Figure 7 shown further through its process of manufacture; Figure 9 is a representation of the thread of the tip of the screw in Figure 1 showing superimposed thereon the profile of the part-formed tip shown in Figure 7; 15 Figures 10A to 10H are successive views of a fastener of the type shown in Figure 1 as it is being used to affix a profiled architectural sheet to a steel batten support member; Figure 11 is a side elevation view of a length of main thread for a fastener according to another embodiment of the present invention; 20 Figure 12 is a detail view in cross section of the thread form in Figure 11; Figure 13 is a side elevation view of a length of main thread which may be used as an alternative to the thread shown in Figure 11; Figure 14 is a detail view in cross section of the thread form in Figure 13; Figure 15 is a side elevation view of a length of main thread which may be used as 25 a further alternative to the thread shown in Figure 11; Figure 16 is a detail view in cross section of the thread form in Figure 15; and Figure 17 is a diagrammatic illustration of the engagement of a portion of a fastener, having a thread as shown in Figure 11, with a thin metal structural member to which it is fastened. 30 WO 2006/043169 PCT/IB2005/003163 9 Description of the Preferred Embodiment and Other Examples of the Invention Referring to Figures 1 to 9, the screw 2 has an elongated cylindrical shank 6 with a longitudinal axis 7, and an enlarged head 8 at one end. The head has a hexagonal top 5 10, for engagement with a driving tool (not shown), and an integrally formed collar 12. At the other end of the shank 6 the screw 2 has a leading point 16 which includes a drilling tip 18. An annular recess 13 is provided under the collar 12 to locate an elastomeric washer 10 11 which extends into the recess 13 and protrudes outwards from the recess. This provides a seal against water when the fastener is installed. The cross section view in Figure 2 shows the washer 11 on the left hand side of the drawing, but on the right hand side, the washer 11 is omitted to better show the recess 13. 15 Towards the leading point 16, the shank 6 carries a main thread 14. This is a single start helical thread which has a helical ridge 20 rising from a cylindrical core 22. The core 22 defines the minor diameter 23 for the main thread, and the crest 24 of the ridge 20 defines the major diameter 25 for the main thread 14. The pitch of the main thread 14 remains constant over its full length. The form of the main thread 14 is 20 such that the core 22 is clearly visible between turns of the ridge 20. The amount of the core's surface which is visible between the turns of the ridge 20 is about the same as the amount of the core which is covered by the thread ridge. The shank 6 has six distinct zones along its length. Commencing from the leading 25 point 16 of the screw and working towards the head 8, these zones are respectively a tip zone 26, a main thread forming zone 28, a main thread zone 30, a knurled zone 32, an unthreaded plain shank zone 33, and a secondary thread zone 34. In order to explain the extent of these zones, this description will refer to "pitch lengths" or "pitches" as a unit of length. That unit is the pitch of the thread which, for a single 30 start thread, is equal to the distance between successive crests 24 when measured in the direction of the longitudinal axis 7 of the screw. When applied to a fastener according to this embodiment having a 14 gauge screw shank (with a core diameter or WO 2006/043169 PCT/IB2005/003163 10 minor diameter of nominal 4.6mm, a major diameter of nominal 6.3mm, and 14 threads per inch) the pitch length would be about 1.8mm. The tip zone 26 extends lengthwise along the shank for about one to two pitches, the 5 main thread forming zone 28 for about one pitch, the main thread zone 30 for about nine to ten pitches, the knurled zone 32 for about one to two pitches, the plain shank zone 33 for about one pitch, and the secondary thread zone 34 for about 3 pitches. A fastener having this configuration and a pitch length of 1.8mm would suit the fastening of a steel sheet profile having a profile height of 19mm to 27mm. The 10 dimensions of the screw would be different for a different profile height; for example a screw to suit a 24mm profile height may have the length of the plain shank zone 33 increased by 5mn. In the tip zone 26, the drilling tip 18 is of the kind having a generally cylindrical cross 15 sectional shape but having two diametrically opposed flutes 42, which extend generally in the axial direction of the screw 2. The terminal end of the tip 18 is formed by two sloping end faces 44, and a substantially straight cutting edge 46 is formed at the junction between each face 44 and a respective one of the flutes 42. 20 The drilling tip 18 in this embodiment has the general form of a twin-fluted steel drilling tip. Although self drilling fastener tips of this general type are generally well known in the threaded fastener industry, drilling tip 18 has significant differences to such well known tips. The diameter of the tip zone 26 is smaller than that of such a tip which would normally be used on a screw having the size of main thread 14 25 chosen. Also, the size of the cutting tip angle 0 is different to that normally used, and the thread rolled onto the main thread-forming zone 28 extends down over portion of the drilling tip 18 such that the flutes 42 intersect the tapered thread 15 in the thread forming zone so the thread in the thread-forming zone is discontinuous. 30 In prior art examples of self drilling fasteners incorporating this general type of drilling tip, the cutting tip angle 0 is almost universally close to 120*. However the preferred embodiment in Figure 4 has 0 = 1350. It has been found that this provides a WO 2006/043169 PCT/IB2005/003163 11 surer start to the drilling process when the sheet metal being drilled is less stiff (due to being thinner) than previously used. The wider angle provides a lower tendency for the tip to "wander" on the metal surface before penetration commences. The invention preferably uses a value for 0 in the range of 1300 to 150* and preferably in 5 the range of 1300 to 1450 and more preferably in the range 130" to 140. Over the length of the main thread zone 30, the core 22 is of uniform diameter (the core diameter 23) and the thread ridge 20 rising from it is of uniform height. Over the length of the secondary thread zone 34, the core 36 is of uniform diameter and the 10 thread ridge 38 rising from it is of uniform height except for a short lead-in 39 where the ridge 38 rises from the unthreaded plain shank zone 33. Linking the core 22 of the main thread zone with the smaller diameter tip zone 26, the core of the main thread forming zone 28 is conically tapered at an angle shown as a 15 on Fig. 7. The taper angle a used in this embodiment is 550 but this may be chosen from the preferred range of 300 to 60'. In the main thread forming zone 28 the thread 15 is tapered. The height of the thread ridge 29 increases gradually over a full single turn until, at the head end of the zone 20 28, the thread 15 in that zone has reached its maximum diameter and becomes the main thread 14. That maximum diameter of the main thread 14 is the major diameter 25 of the main thread while the core 22 defines the minor diameter 23. These major and minor diameters are substantially constant over the main thread zone 30. 25 In use, the thread forming zone 28 expands the diameter of the hole by plastically deforming the metal immediately surrounding the hole. As the diameter expands, the metal so displaced increases the thickness of the thin metal sheet immediately surrounding the hole. 30 At the tip end of the secondary thread zone 34, the ridge 38 of the secondary thread 40 gradually rises from zero to its maximum height over a single turn towards the head 8. So the diameter of the secondary thread 40 rises, over the length of that single turn, WO 2006/043169 PCT/IB2005/003163 12 from the diameter of the core 36 adjacent the unthreaded zone 33 to its maximum outside diameter (its major diameter) near the head 8. This provides a lead in 39 by which the secondary thread 40 can engage the metal of the sheeting. 5 The main thread 14 and the secondary thread 40 each have the same respective nominal major diameter and nominal minor diameter, but there is a difference in the pitch. The secondary thread 40 is a coarser pitch than main thread 14. The main thread 14 has a pitch of 14 TPI while the secondary thread has a pitch of 12 TPI. 10 The knurled zone 32 is occupied by a cogged generally gear-wheel-shaped portion having an array of parallel valleys 56 and ribs 58 each aligned in the direction of the axis 7. The valleys 56 are about as deep as the core 22 of the main thread but the ribs 58 are substantially shorter than the ridge 38 of the secondary thread. The knurled zone 32 is formed by pressing the valleys 56 into the shank 6 in order to displace 15 metal therefrom into the axially aligned ribs 58. In other embodiments the valleys may be deeper than the core. The function of the knurled zone 32 is to lightly ream out the hole formed in the sheeting by the main thread 14 and to do so before the secondary thread 40 engages 20 the hole. The knurled zone contacts only the most inwardly projecting metal, but by its action any burr remaining at or around the hole from the hole drilling operation, and the formation of the thread within that hole, is removed or reshaped by the knurled zone. The preferred sizing of the knurled zone for this purpose is discussed later in this specification. 25 The shape of the thread ridge 20 in the main thread zone 30 is shown in detail in Figure 6. The ridge 20 rising from the cylindrical core 22 has a head-side flank 62 (also called the trailing flank) and a tip-side flank 64 (also called the leading flank) on respective sides of a crest 66. The head-side flank 62 is inclined at an angle y of 20' 30 to a plane normal to the screw axis 7 and the tip side flank 64 is inclined at an angle 8 of 350 to the axis 7. These two angles may be varied a little (for example y may be in the range 10* to 30*, preferably 150 to 25*; and y may be in the range 250 to 450, WO 2006/043169 PCT/IB2005/003163 13 preferably 30* to 400). The angle P included between the flanks 62 and 64 is preferably in the range 450 to 65" and is 550 in the embodiment illustrated. In order to provide the greatest pull-out strength, it is desirable for y to be as small as 5 possible. Pull out performance drops off significantly if y is greater than 25*. But if y is too small then it has been found that vibration tends to loosen the fastener too easily. There is thus a conflict of demands that must be addressed when selecting a value for y. The aim of improved pull-out strength together with vibration resistance is achieved with alternative preferred thread forms described later in this specification 10 with reference to Figures 11 to 16. To maximise pull-out strength, it is desirable to have the major diameter 25 of the main thread 14 as large as possible. It is also desirable to have the height of the threadform as large as possible. The preferred embodiment has achieved this by 15 having the major diameter of the main thread 14 corresponding to that of a 14 gauge screw even though the hexagonal drive top 10 on the head 8 corresponds to that nonnally used on a 12 gauge screw. The plain shank zone 33 carries neither thread nor indentations and extends from 20 where the end of the secondary thread 40 blends down to the core at the head-side shoulder 60 of the knurled zone 32. The length chosen for this plain shank zone 33 is a function of the length of the screw, which is in turn defined by the height of the profile ribs on the sheet metal being fastened to the underlying battens. While different screw lengths are required for different applications, the manufacturing of 25 such different lengths may be conveniently achieved by adjusting the length of the plain shank zone 33 and keeping the lengths of the other zones common for all lengths of screws. This would minimize the inventory of die components required for manufacturing a variety of screw lengths. 30 However it is not essential that the plain shank zone 33 be present at all, and it can alternatively be located between the main thread zone 30 and the knurled zone 32. This would provide an advantage that the sheet metal roofing cannot then be pulled WO 2006/043169 PCT/IB2005/003163 14 hard against the knurled zone by the main thread if the cutting tip is slow in drilling through a batten. Alternatively a plain shank zone may be located on both sides of the knurled zone 32. 5 Along the full length of the threads 14 and 40, the core 22 is preferably circular but it may alternatively have a lobed cross section when viewed axially. The steps in using the screw 2 to fasten a panel of profiled metal roofing sheeting to 10 an underlying thin metal batten will now be described: (a) The hexagonal top 10 of the screw is engaged with a driving tool and rotated with the drilling tip 18 in contact with the sheeting being fastened. Pressure is applied towards the tip 18 throughout the remainder of the fastening process. 15 (b) The tip 18 cuts its way through the sheeting, creating a hole in the sheeting substantially equal to the diameter of the tip 18. This diameter is significantly less than the diameter required for unhindered passage of the main thread 14 through the hole. (c) The tapering main thread forming zone 28 then passes through the hole 20 in the sheeting and, as it does so, it plastically deforms the metal sheeting at the perimeter of the hole to make the hole larger and form a thread therein. The portion of metal so deformed to enlargen the hole is displaced axially of the hole (ie. laterally of the substrate sheet metal) to in effect thicken the metal sheeting adjacent the hole. This 25 provides additional sheet material with which the fastener's thread can engage and thus strengthen the fastening. (d) The main thread zone 30 then passes through the hole in the sheeting. (e) Then the knurled zone 32 passes through the hole in the sheeting and its ribs 58 clean off burrs and swarf remaining from the hole drilling 30 and thread forming operations.

WO 2006/043169 PCT/IB2005/003163 15 (f) Soon thereafter, the secondary thread 40 engages the hole through the roofing panel so that the panel is restrained from downward movement towards the tip end. (g) At some time about when the knurled zone 32 passes through the hole 5 in the sheeting, the tip 18 contacts the batten and commences the process of drilling a second hole, this time in the batten, and the main thread forming zone 28 in turn forms a thread in the second hole as occurred with the hole through the metal sheeting panel. (h) Soon after the main thread zone 30 enters the hole in the batten, the 10 collar 12 compresses the washer 11 onto the sheet metal panel and tightening is ceased. The knurled zone 32 does not enter the hole in the batten. By appropriate selection of the diameters, the tip 18 removes just the right. amount of 15 metal so that the subsequent working of the surrounding metal produces the optimum metal thickness for engagement with the main thread 14. Similarly, the outside diameter of the knurled portion is chosen to satisfactorily remove any burrs or swarf material while still leaving sufficient metal for proper engagement with the secondary thread. 20 Burrs formed around the hole during the drilling process can damage the washer 11, or be pressed into the washer, to provide a gap where water may enter. Removal of burrs by the knurled zone 32 overcomes this problem. 25 The outside diameter of the knurled zone is slightly greater than the mean diameter of the main thread, which is the same as the mean diameter of the secondary thread. The mean diameter is calculated as (D 1

+D

2 )/2 where Di is the minor diameter of the main thread and D 2 is the major diameter of the main thread. 30 Preferably the outside diameter of the knurled zone is in the range bounded by:

(D

1 + 0.51(D 2 - DI)) and (D 1 + 0.60(D 2 - DI)) WO 2006/043169 PCT/IB2005/003163 16 Preferably the outside diameter of the knurled zone is greater than or equal to (Di + 0.53(D 2 - Di)). Preferably it is less than or equal to (Di + 0.58(D 2 - Di)). 5 The screw 2 is manufactured from a cold-headed blank in a multi-stage forming operation to produce first the tip (as seen in Figure 7). Then the threads 14 and 40 and the knurled zone 32, followed by appropriate hardening and plating operations. A blank first has a drilling tip 72 formed thereon. The tip 72 is joined by a short 10 tapered portion 74 to the unworked portion 76. The taper angle oc is 55". The part formed fastener at this stage is shown in Figure 7. The diameter of the drilling tip 72 is smaller than the minor diameter of the thread and smaller than would conventionally be applied to a self-drilling screw of the given diameter. The cutting tip angle e is 1350. 15 The two threads 14 and 40 and the knurled zone 32 are then roll-formed onto the screw in a single operation. The die used to roll the main thread 14 onto the shank of the fastener extends from the main thread zone 30 over the tapered portion 74 and portion of the drilling tip 72. As there is insufficient metal to fill the thread rolling 20 dies over the tapered portion 74 and the tip 72, the thread so formed tapers over the tapered portion 74 and the drilling tip 72. As seen in Figure 8, the thread in the main thread forming zone 28 extends into (overlaps) the drilling tip 18. The overlapping zone 27 has the thread cut by the flutes 25 42 on the drilling tip. In Figure 9 the dashed lines indicate the shape and size of the tip zone 26, main thread forming zone 28 and (portion of) the main thread zone 30 at the manufacturing stage shown in Figure 7 while the solid lines indicate the sizes and configurations of the 30 tapered thread 15 and main thread 14 after they are rolled.

WO 2006/043169 PCT/IB2005/003163 17 In Figures 10A to 10H, the successive stages in the fastening process can be seen when using a fastener 2 of the type shown in Figure 1 to affix a profiled architectural sheet 80 to a steel batten 84 which is functioning as a support member for the sheet. 5 The profiled architectural sheet 80 has an array of parallel ribs 81 formed therein, the ribs rising as stiffening means from generally planar valleys 82. Figures 1 OA to 10H show only one of these ribs 81. In Figure 10A the fastener 2 is being rotated with the drilling tip 18 pressed into 10 contact with the top of a rib 81 on the sheet 80. In Figure 10B the drilling tip 18 has cut a hole 86 having the diameter of the drilling tip. The hole is formed by removing metal from the sheet 81. In Figure 1 OC the fastener has been rotated into the hole 86 until the metal in the 15 sheet at the wall 88 of the hole engages with the tapered threaded portion 15 of the fastener. The fastener is rotated further into the hole and this expands the hole by plastic deformation of the metal immediately surrounding the hole, thereby increasing the thickness of the metal immediately surrounding the hole 86 as it increases the diameter of the hole. 20 Continued rotation of the fastener carries it further into the hole 86 until the reaming portion 90 contacts the top of the rib as shown in Figure 10D. As the fastener is rotated further, the reaming portion 90 skims through the hole 86 and, in doing so, increases the diameter of the hole a little. However the diameter so increased is still 25 less than the major diameter of the main thread 14 on the fastener. In Figure 10E the reaming portion 90 is almost completely through the metal of the rib 81 and the drilling tip 18 has contacted the upper surface 85 of the batten 84. Continued rotation causes the drilling tip to then cut a hole 92 in the batten. The hole 30 has the diameter of the drilling tip. This is the position shown in Figure 1 OF.

WO 2006/043169 PCT/IB2005/003163 18 Continued rotation of the fastener causes the tapered threaded portion 15 to engage with the hole through the batten, as seen in Figure 10G. This causes the hole to expand by plastic deformation of the metal immediately surrounding the hole 92 in the batten, thereby increasing the thickness of the metal immediately surrounding the 5 hole as the diameter of the hole increases. This effectively thickens the metal top wall 83 of the batten at the hole 92 where it is needed. At the same time the secondary thread 40 is commencing engagement with the hole 86 through the rib 81. The fastener is tightened to its position shown in Figure 1 OH where the main thread is 10 fully engaged with the batten, and the elastomeric washer 11 is pressed down by the head 8 of the fastener to seal around the hole through the rib 81 and the engagement of the secondary thread with the rib prevents depression of the rib along the shank 6 of the fastener. 15 Although the cutting of the second hole 92 is shown happening after the reaming portion commences the skimming through said first hole 86, the order of these actions could be reversed. Figures 11 and 12 show a screw fastener 102 with a main thread 114 having a thread 20 form which is more preferred for the present invention than is the thread form described above with particular reference to Figure 6. The equilateral triangle shown as dashed lines has included angles of 60" and represents the shape of a standard thread form having both flanks angled at 600 to the axis. 25 As seen in Figures 11 and 12, the ridge 120 of the main thread 114 has a head-side flank 162 which is inwardly curved or dished as seen in cross-section Figure 12. The tip-side flank (leading flank) 164 is outwardly curved or domed. The curvature of flanks 162 and 164 when seen in cross-section is circular and the flanks meet at the crest 166 at an angle of approximately 600. 30 As can be seen from Figure 12, the innermost portion 168 of the head side flank 162 rises from the core 122 initially at an angle of 300 to the axis 107 and then gently WO 2006/043169 PCT/IB2005/003163 19 curves, changing direction towards the perpendicular to the axis 107. At the mean thread diameter 172 of the thread the flank 162 is sloping at about 60" to the axis 107. From there on outwards, the slope of the flank 162 relative to the axis 107 continues to increase, rising from 60" to almost 900 at the crest 166. 5 The tip-side flank 164 rises from the core 122 initially at approximately 90" to the axis and then curves gently towards the screw's head until, at the mean thread diameter 172, it is sloping at about 600 to the axis 107. The tip-side flank 164 then continues to curve over until, when it reaches the crest 166, it is sloping at about 300 10 to the axis 107. By means of the varying slopes over each flank, the innermost portion 168 of the thread near the core 122 has the tip-side flank 164 sloping at closer to 900 to the axis than is the head side flank 162, whereas for the outermost portion 170 of the thread near the crest 166, the head side flank 162 slopes at closer to 900 to the axis than does the tip-side flank 164. 15 The above-described gradation in the slope of the head side flank 162 simultaneously and beneficially provides two performance characteristics of the thread form which have previously been not available together. The shallow slope of the innermost portion 168 of the head-side flank 162 improves resistance of the fastener to 20 loosening during vibration conditions, while the steep angle of the outermost portion 170 provides for improved pullout strength of the fastener. The thread and thread form illustrated on the fastener 202 in Figures 13 and 14 have, like those in Figures 11 and 12 a dished head-side flank 262 and a domed tip-side 25 flank 264 rising from the core 222 to the crest 266. While for Figures 11 and 12 the curvature of the flanks is circular, in the case of Figures 13 and 14 the curvature is parabolic and somewhat deeper. The threads 114 and 214 exhibit a similar improvement in pullout and vibration resistance performance when compared with the thread shown in Figure 6. 30 The thread and thread form illustrated on the fastener 302 in Figures 15 and 16 have a head side flank 362 and a tip-side flank 364 which are also dished and domed WO 2006/043169 PCT/IB2005/003163 20 respectively, broadly similarly to that shown in Figure 13. However in the case of Figures 15 and 16, a curvature of the flanks is approximated by a pair of flat flank portions 368 and 370. For the head side flank 362, the innermost portion 368 is sloped at 350 to the axis 307 while the outermost portion 370 is sloped at 80* to the 5 axis. On the tip-side flank 364, the innermost portion 374 is angled at 850 to the axis 307 while the outermost portion 376 of the flank is angled at 50" to the axis. It can be seen from Figure 14 that the position where the head side flank 262 transitions through an angle of 60* relative to the axis 207 is closer to the axis than is 10 the position where the tip side flank 264 transitions through an angle of 600 relative to the axis 207. Similarly it is observable from Figure 16 that the position where the head-side flank 362 transitions through an angle of 600 relative to the axis 307 is closer to the axis than is the position where the tip side flank 364 transitions through an angle of 60* relative to the axis. Although not as immediately apparent, the same 15 condition applies to the threadform in Figure 12. However the average slope of the head side and tip-side flanks 62 and 64 are each about 600 to the axis 7. 20 In Figures 12, 14 and 16 the dashed lines indicate the thread form of a symmetrically flanked thread with each flank aligned at an angle of 60" to the axis of the respective fastener. In Figure 17 the fastener 102 has been fastened to the wall of a support member 190 25 which is formed from thin metal sheet. The drilling tip has formed an initial hole which has then been expanded by plastic deformation of the surrounding metal as the tapered portion of the fastener penetrated into the hole. The plastic deformation has created a bulge 192 directed from the surrounding plane of the member 190 towards the leading tip of the fastener. It has also created a bulge 194 directed towards the 30 head end of the fastener. The effect of the bulges 192 and 194 in combination means that the thickness of the metal surrounding the hole is therefore significantly increased from the initial thickness of the member 190.

WO 2006/043169 PCT/IB2005/003163 21 As seen in Figure 17, the dished curvature of the trailing flank 162 neatly fits the curvature induced in the metal when forming the bulge 192. Close to the core 122, the head-side flank 162 engages the bulge 192 at an angle that is shallow relative to 5 the axis 107. Close to the crest 124, the head-side flank 162 engages the bulge 192 at an angle that is close to 900 relative to the axis 107. By engaging the bulge 192 over a varying angle relative to the axis 107, the fastening therefore exhibits the high stress handling advantages of a head-side flank sloping at a large angle to the axis 107 plus the vibration resisting advantages of a head-side flank sloping at a shallow angle to 10 the axis 107. Previously there has needed to be a trade-off between these two characteristics. Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions 15 may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention. For example the support member may be something other than a metal batten formed from sheet steel. 20 It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features. 25 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge in Australia.

Claims (20)

1. A screw fastener for attaching a profiled sheeting panel to a support, said fastener having: 5 (i) an elongate shank; (ii) an enlarged head at one end of the shank adapted for engagement with a driving tool; (iii) a drilling tip on the other end of the shank adapted to drill a hole of a first diameter; 10 (iv) on the shank a first threaded portion adapted to screw into said support, said first threaded portion having a first thread, the crest of said first thread defining a major diameter of the first thread, and the root of said first thread defining a minor diameter of the first thread; (v) said drilling tip sized such that said first diameter is in the range of 60% to 15 85% of the minor diameter; (vi) a tapered portion joining the drilling tip to the first threaded portion said tapered portion having a tapered thread thereon, said tapered thread having a thread height which increases from the drilling tip to said first threaded portion; 20 (vii) on the shank a second threaded portion adapted to engage a crest of said panel; and (viii) a reaming portion located between the first threaded portion and the second threaded portion, said reaming portion having an outside diameter less than said major diameter of the first thread. 25

2. A fastener according to claim 1 wherein said drilling tip has a generally cylindrical cross section and two diametrically opposed flutes which extend in the axial direction of the fastener. 30

3. A fastener according to claim 2 wherein said flutes intersect thread formed on the drilling tip. WO 2006/043169 PCT/IB2005/003163 23

4. A fastener according to claim 2 or 3 wherein each said flute terminates at a cutting edge said cutting edges subtending therebetween an angle in the range 130* to

1500.

5 5. A fastener according to any one of claims 1 to 4 wherein an elastomeric washer is fitted on the shank adjacent said head.

6. A method of fixing a profiled architectural sheet to a support member whereby a threaded fastener passes through said sheet and into the support member, said 10 fastener comprising: - an elongate shank having an enlarged head at one end and a drilling tip on its other end; - a first threaded portion positioned towards said other end, the thread of said first threaded portion having a major diameter and a minor diameter; i5 - a second threaded portion separated from said first threaded portion and located between said head and said first threaded portion; - a tapered threaded portion adjacent and between the drilling tip and the first threaded portion; and - a reaming portion located between said first threaded portion and said 20 second threaded portion; said method comprising: (i) rotating the fastener with said drilling tip pressed into contact with a rib on said sheet; (ii) causing the drilling. tip to cut a first hole of a first diameter by removing 25 metal from said sheet; (iii) rotating the fastener into the first hole to engage said tapered threaded portion with said sheet; (iv) rotating the fastener further into the first hole to expand said first hole by plastic deformation of the metal immediately surrounding the hole, thereby 30 increasing the thickness of the metal immediately surrounding the hole and increasing the diameter of the hole; (v) continuing to rotate the fastener into the first hole, thereby: WO 2006/043169 PCT/IB2005/003163 24 - skimming the reaming portion through said first hole to increase the diameter of the hole to less than said major diameter, and - causing the drilling tip to cut a second hole of said first diameter in the supporting member; 5 (vi) continuing to rotate the fastener further into said second hole to engage said tapered threaded portion with the support member; (vii) continuing to rotate the fastener further into the second hole to expand the second hole by plastic deformation of the metal immediately surrounding the second hole, thereby increasing the thickness of the metal immediately 10 surrounding the second hole and increasing the diameter of the second hole; and (viii) continuing to rotate the fastener into the first and second holes to thereby engage said first threaded portion with said supporting member and engage said second threaded portion with said sheet. 15

7. A method according to claim 6 wherein the cutting of said second hole by the drilling tip commences before the reaming portion commences the skimming through said first hole. 20

8. A method according to claim 6 wherein the cutting of said second hole by the drilling tip commences after the reaming portion commences the skimming through said first hole.

9. A method according to any one of claims 6 to 8 wherein said drilling tip has a 25 generally cylindrical cross section and two diametrically opposed flutes which extend in the axial direction of the fastener.

10. A method according to claim 9 wherein said flutes intersect thread formed on the drilling tip. 30 WO 2006/043169 PCT/IB2005/003163 25

11. A method according to any one of claims 9 or 10 wherein each said flute terminates at a cutting edge said cutting edges subtending therebetween an angle in the range 1300 to 150". 5

12. A method according to any one of claims 9 to 11 wherein an elastomeric washer is fitted on the shank adjacent said head, said washer being pressed into contact with said sheet to form a weatherproof seal around said first hole.

13. A method of manufacturing a self drilling threaded fastener including: 10 - forming a tipped blank having an unthreaded shank, an enlarged head at one end and a drilling tip at the other end, said drilling tip having a generally cylindrical cross section of diameter smaller than the diameter of said unthreaded shank, said drilling tip having two diametrically opposed flutes which extend in the axial direction of the fastener, and said drilling 15 tip being joined to said unthreaded shank by a tapered portion; and - roll forming onto said tipped blank: - a first threaded portion toward the tip end of said tipped blank, - a second threaded portion toward the head end of said tipped blank, and 20 - a knurled portion located between the first and second threaded portions and having the size of its outside diameter between the minor diameter of the first threaded portion and the major diameter of the second threaded portion; wherein said first threaded portion includes: 25 - a third threaded portion having a parallel thread formed onto said shank, - a fourth threaded portion formed onto said drilling tip and intersected by said flutes, and - a tapered threaded portion joining said third and fourth threaded portions. 30

14. A self-drilling threaded fastener adapted for fastening a high strength sheet steel architectural panel to a support, and having a drilling tip wherein the drilling tip comprises a portion having two diametrically opposed flutes which extend generally WO 2006/043169 PCT/IB2005/003163 26 in the axial direction of the screw, each said flute terminating at a cutting edge, said cutting edges subtending therebetween an angle in the range 130' to 150".

15. A fastener according to claim 14 wherein said angle is in the range 1300 to 145*. 5

16. A fastener according to claim 15 wherein said angle is in the range 130* to 140".

17. A screw threaded fastener including an elongate shank having a longitudinal axis, an enlarged head at one end of the shank, a leading tip at the opposite end of the 10 shank, and a screw thread extending over at least a part of the length of the shank, wherein the screw thread includes: - a root and a crest; - a leading flank rising from the root and directed away from the leading tip and sloping outwardly relative to the longitudinal axis at a varying angular 15 disposition relative to the longitudinal axis; - a trailing flank rising from the root and directed away from the head and sloping outwardly relative to the longitudinal axis at a varying angular disposition relative to the longitudinal axis, - said leading flank and trailing flank joining at said crest of the screw 20 thread; wherein: - the angular disposition of the leading flank relative to the longitudinal axis changes between the root and the crest from greater than 450 nearer the root to less than 45" nearer the crest; and 25 - the angular disposition of the trailing flank relative to the longitudinal axis changes between the root and the crest from less than 45" nearer the root to greater than 45" nearer the crest.

18. A fastener according to claim 17 wherein said angular disposition of a flank 30 relative to -the longitudinal axis changes gradually, whereby that flank has a gradually curved form when viewed in cross section longitudinal to said axis. WO 2006/043169 PCT/IB2005/003163 27

19. A fastener according to claim 18 wherein said angular disposition of both said leading and trailing flanks relative to the longitudinal axis change gradually, whereby both said flanks have a gradually curved form when viewed in cross section longitudinal to said axis. 5 20. A fastener according to claim 18 or 19 wherein the rate of change of the angular disposition of a said flank or flanks relative to the longitudinal axis is/are substantially constant so that that said flank or flanks appear to be uniformly curved from their root to their crest. 10 21. A fastener according to claim 17 wherein said angular disposition of a said flank relative to the longitudinal axis changes abruptly, whereby that flank has a non uniformly curved form when viewed in cross section longitudinal to said axis. 15 22. A fastener according to claim 21 wherein said angular disposition of both said leading and trailing flanks relative to the longitudinal axis change abruptly, whereby both said flanks have a non-uniformly curved form when viewed in cross section longitudinal to said axis.

20 23. A fastener according to claim 21 wherein said flank is faceted and has a facet edge extending along the thread in a helical direction coaxial. with said longitudinal axis. 24. A fastener according to any one of claims 17 to 23 wherein the trailing flank 25 appears dished. 25. A fastener according to any one of claims 17 to 23 wherein the trailing flank is concave from said root of the thread to the crest of the thread. 30 26. A fastener according to any one of claims 17 to 23 wherein the trailing flank has a plurality of generally flat segments when viewed in cross section. WO 2006/043169 PCT/IB2005/003163 28 27. A fastener according to any one of claims 17 to 26 wherein the leading flank appears vaulted. 28. A fastener according to claim 27 wherein the leading flank has a domed or 5 gently convex form when viewed in cross section. 29. A fastener according to claim 27 wherein the leading flank comprises a plurality of generally flat segments when viewed in cross section.